Heavy hydrocarbons in the form of petroleum deposits are distributed worldwide and the heavy oil reserves are measured in the hundreds of billions of recoverable barrels. Because of the relatively high viscosity, these crude deposits have extremely low mobilities and have low recoveries using conventional primary and secondary means. For many heavy oil fields, the only economically viable means of oil recovery is by the addition of heat and or solvent(s) to the oil deposit, which significantly decreases the viscosity of the oil and allows the oil to flow from the formation into the producing wellbore.
The most significant oil recovery problem with heavy oil, tar sands and similar hydrocarbonaceous material is the extremely high viscosity of the native hydrocarbons. At reservoir conditions, the oil viscosity ranges from 10,000 cp at the low end of the range to 25,000,000 cp plus at the high end. The viscosity of steam at injection conditions is about 0.020 cp to 10 cp, depending upon the temperature and pressure of the injected steam. Assuming similar rock permeability to both phases steam and oil, then the viscosity ratio provides a good measure of the flow transmissibility of the formation to each phase. Under the same pressure gradient, gaseous steam can therefore flow from 500,000 to 250,000,000 times easier through the material than the oil at reservoir conditions. Because of this viscosity ratio, it is imperative and critical to any recovery application that the steam be confined or limited to an area of the reservoir by a seal. This seal can be physical, hydraulic or pneumatic and essentially must provide a physical situation which guarantees no-flow of any fluid across an interface. This can be implemented by several means. Without this “barrier” the steam will bypass, overrun, circumvent, detour around the cold viscous formation and move to the producer wellbore.